Conventionally, so-called battery "fuel gauges" have been used to track battery current consumption and to manage power in portable, battery-operated devices. Some such power management schemes operate as software tasks by directly measuring on-times of various current-consuming subsystems or modules such as modems and RS-232 interfaces, logic circuitry and power-down, or sleep mode, circuitry. Such conventional method and apparatus are described in U.S. Pat. No. 4,724,528 which issued Feb. 9, 1988 and which is subject to common ownership herewith. Because they rely on direct and/or durational measurements, such method and apparatus inaccurately would predict remaining battery capacity in an ink-jet printer, wherein current consumption is highly variable, e.g. duty cycle- or usage-dependent.
For example, in ink-jet printers providing draft as well as letter quality printing options, carriage on-time measurements would overstate the ink-jet firing and carriage motor currents consumed during draft printing relative to letter quality printing. Similarly, in ink-jet printers equipped with monochrome as well as tri-color pen printheads, printhead on-time measurements would overstate the printhead current consumed during black printing relative to color printing. In other words, with conventional method and apparatus, battery current consumption tracking is dependent upon many variables such as print quality selections, e.g. draft versus letter; pen selections, e.g. black versus color; color reproduction techniques, e.g. error diffusion versus shingling; and sheet advance modes, e.g. automatic versus manual.
Ink drop count-based printer control has been proposed, for the purpose of managing time-averaged power drain on a printer's power supply and for the purpose of increasing printer throughput by servicing pens at optimum times. Such method and apparatus are described in co-pending U.S. patent application Ser. No. 07/951,255 entitled "DROP COUNT-BASED INK-JET PRINTER CONTROL METHOD AND APPARATUS, which is subject to common ownership herewith. The disclosure of that application is incorporated herein by this reference. In accordance with these method and apparatus, the number of firings of each ink-jet pen in the printhead is maintained in memory by the printer's microcontroller or other drop count means, and carriage control is based at least in part thereon. But there is no concern with battery operation, drain thereon or remaining capacity thereof.